Method of forming graphite articles



United States Patent 3,300,550 METHOD OF FORMING GRAPHITE ARTICLES Raymond Leslie Bond, Chessington, Frank James Pinchin, Ewell, and Mansel John Jenkins, Culcheth, Warrington, England, assignors to United Kingdom Atomic Energy Authority, London, England Filed Jan. 25, 1965, Ser. No. 427,626 Claims priority, application Great Britain, Feb. 3, 1964,

. 4,575/64 2 Claims. (Cl. 26429) The present invention relates to the manufacture of graphite and to graphite articles produced thereby.

According to the invention, there is provided a method of manufacturing a graphite article in which a coke grist is mixed to form a hot formable mass with a chloroform extract of coal, such mass being subsequently formed to the desired shape, baked and graphitized. This method derives from a conception of an extraction substance being able to isolate from such a complex carbonaceous material as coal those components which will lend themselves to the achievement of certain desired properties in graphite manufacture. Thus we have found that the use of a chloroform extract of shock-carbonized coal as a binder achieves in the graphite product a remarkable uniformity of size of the openings giving access to open porosity in the graphite. This latter property is considered to be advantageous for securing low open pore volume by means of impregnation because an impregnant chosen with regard to the mean pore entrance diameter can be expected to behave similarly, and hence more effectively, on practically all the open pores.

Chloroform is one of many solvents that have been used with coal by research workers in the past; other solvents include phenol, pyridine and benzene. There has been seen in this work the possibility of substantially de-ashing coal. The chloroform extract, for the purpose of this invention, is not limited to any particular kind of coal although there is a preference for chloroform soluble material of the kind extracted from a shock-heated coking coal (Dryden and Joy, Fuel 1961, 40, 473). Material similar in properties may be produced by chloroform extraction of lower rank coals after mild treatment in hydrogen (McConnell and Pinchin, Fuel, 1961, 40, 81; Taits, Bronovets and Andreeva, Khim i Tekhnol Topliva i Masel, 1963, 8, 24) with or without shock heating. The softening point of the extract is the important factor, and this should be between about 50 and 180 C. By the above methods a maximum yield of suitable extract may be obtained.

The chloroform extract is therefore preferably obtained from coal which has previously been shock heated, that is to say, preheated to a temperature of .at least 350 C. The preheating temperature is preferably somewhat in excess of 400 C. Such preliminary treatment is aimed to secure the maximum yield of suitable extract.

The following is given merely as an illustration of the invention:

Example The coal employed in this examplewas of high rank (National Coal Board Ranke Code 301) and metabituminous according to Seylers classification; its source was the S. Garesfield (Durham) Colliery and the ultimate analysis (dry ash free) was:

C 89.2 H 5.1 N 1.4 S 0.7 O 3.6 CI 0.02

When already ground to pass a 72 B.S. mesh sieve 3,300,550 Patented Jan. 24, 1967 with between 30 and 50% also capable of passing a 240 B.S. mesh sieve, the coal was shock-heated by way of preliminary treatment to a temperature of about 420 C. The heating and cooling cycle defining this treatment was as follows: The coal was contained in a quartz tube, and this tube was plunged into an electrically heated salt bath (containing f-used potassium nitrate and sodium nitrite) at 420 C.; after 30 minutes the tube was removed and shock cooled by plunging into cold water.

Prior to extraction, the shock-heated coal was dried at C. in a vacuum of 1.5 mm. of mercury. The solvent was commercially obtained chloroform stabilized by an addition of 1% by weight of ethanol. The extraction was carried out at the boil in a battery of Soxhlet apparatus for a period of about 100 hours and the resulting solution was concentrated. The percentage extraction into the solvent was approximately 10% by weight. An analysis of the extract gave the following results:

The moisture content is the weight loss in nitrogen at C. at which temperature the extract had softened.

Mixes of extract with a calcined R coke grist were made in a mechanical pestle and mortar, the proportions being 84 parts of the extract to 300 parts of the grist. The particle size distribution for the grist was:

Percent Above 36 B.S. mesh 16 60-120 B.S. mesh 18 300 B.S. mesh 16 Through 300 B.S. mesh 50 This mix was moulded into an artefact under a pressure of 20 tons/sq. inch at C. and carbonised by heating to 920 C. at a rate of temperature rise not exceeding 6 C. per hour. The carbonised artefact was then graphitized by heating to about 2,800 C. in a graphite tube furnace, this temperature being reached in a period of 3 /2 to 5 days and being held over a period of from two to four hours. Cooling took about 2-3 days down to 1,000 C.

Measurement of the bulk and helium densities of the graphitized article gave values of 1.53 and 2.20 gm./cc. respectively from which the volume percentage of open pores was deduced as being about 30%. Although this figure for the open porosity may appear large, the remarkable finding is the high degree of uniformity in size of the openings giving access to this porosity. The test for this parameter was carried out with a mercury porosimeter by which values are derived for the cumulative volumes of mercury which are impressed into a graphite sample under a number of different applied pressures. The result indicated that about 85% of the open porosity is accessible through entrance diameters lying in the narrow range of 2 to 6 microns, and that less than 3% is associated with diameters in excess of 10 microns. A fuller representation of the spectrum of entrance diameters is given by the curves in the accompanying drawing where the apparent cumulative volume of impressed mercury as a percentage of graphite bulk volume is plotted against a scale of entrance diameters obtained by direct conversion from the mercury pressures. The full line marked 1 is in respect of the graphite prepared by this example, While those marked 2, 3 and 4 are in respect of graphites which were similarly prepared but had instead of the chloroform extract binder an anthracene oil extract of various coals, namely, in the case of a 2 a Maltby coal (NCB code 601) which is par-abituminous, in the case of 3 a Rossington coal (NCB code 801) which is metalignitous, and in the case of 4 a Manor coal (NCB code 602) which again is parabituminous.

Using the method of the invention the range of entrance diameters for a graphite artefact may be shifted but still restricted in scope by adjusting the particle size distribution in the initial coke grist. In general the finer the particle size the smaller the mean entrance diameter. For reduction of the open porosity in the graphitized product in accordance with the invention single or multiple impregnation may be included, conventionally between the stages of baking and graphitization. Generally speaking the impregnant would be a low melting point solid hydrocarbon, such as pitch tar. In the case of multiple impregnations the artefact is rebaked before any succeeding impregnation. sir-able for nuclear grade graphite.

We claim:

1. A method of manufacturing a graphite article com- A low value of open porosity is particularly de- 20 prising the steps of mixing a coke grist with a chloroform extract of coal to form a hot, formable mass, forming the mass to the desired shape and baking and graphitizing the mass.

2. A method of manufacturing a graphite article according to claim 1 including the intermediate steps between baking and graphitizing of impregnating the mass with a low melting point solid hydrocarbon and rebaking the mass.

References Cited by the Examiner UNITED STATES PATENTS 2,637,072 5/1953 Greaves et al. 26429 2,838,808 4/1959 Sem 26429 3,089,195 5/1963 Woodburn 264-29 FOREIGN PATENTS 1,274,040 9/ 1961 France.

ROBERT F. WHITE, Primary Examiner.

J. A. FINLAYSON, Assistant Examiner. 

1. A METHOD OF MANUFACTURING A GRAPHITE ARTICLE COMPRISING THE STEPS OF MIXING A COKE GRIST WITH A CHLOROFORM EXTRACT OF COAL TO FORM A HOT, FORMABLE MASS, FORMING THE MASS TO THE DESIRED SHAPE AND BAKING AND GRAPHITIZING THE MASS. 